Project Summary/Abstract With an increased recognition of the chronic relapsing nature of drug addiction, national efforts are being made to foster the redesign and development of recovery-oriented system of care in order to support sustained recovery. There is a clear need to develop a comprehensive measurement tool that captures the multidimensionality of recovery. Meanwhile, awareness of the enormous advantages of Item Response Theory (IRT) is growing rapidly in the behavioral research community. The goal of this proposed project is to use IRT to help develop, evaluate, and provide initial validity evidence for a measure of recovery. To achieve this goal, we will conduct secondary analyses on data collected in the national Drug Abuse Treatment Outcome Studies (i.e., DATOS that includes adult patients, and DATOS-A that includes adolescent patients) which contain a comprehensive set of measures pertinent to recovery. The project is organized around three specific aims. We will apply IRT methods to screen and identify potential items that can enhance the measurement of recovery from the existing pool of measures in DATOS (Aim 1). We will investigate potential measurement non- invariance in the developed recovery scale across subgroups defined by gender or age (Aim 2). We will also obtain initial validity evidence of the developed recovery scale via longitudinal data analysis (Aim 3). The application of the state-of-the-art IRT methodology will lead to a recovery measure that is psychometrically sound, forming a solid foundation that can be continuously improved upon. In addition, the application of IRT to solve measurement problems in addiction research is not only substantively innovative, but would lead to significant opportunities for methodological advancements as well. Taken together, we believe the proposed study has the potential for making significant unique contributions to drug addiction research, treatment and evaluation, and to the IRT methodology in behavioral measurement.